6.
Setting the SQL Join Syntax

Object queries often involve using SQL joins behind the scenes. You can
configure OpenJPA to use either SQL 92-style join syntax, in which joins are
placed in the SQL FROM clause, the traditional join syntax, in which join
criteria are part of the WHERE clause, or a database-specific join syntax
mandated by the
DBDictionary. OpenJPA only supports outer joins when using
SQL 92 syntax or a database-specific syntax with outer join support.

The
openjpa.jdbc.DBDictionary plugin accepts the
JoinSyntax property to set the system's default syntax. The available
values are: